The plaintiffs claim that although the company’s Marlboro Light cigarettes were advertised to contain lower levels of tar and nicotine, they were made with the same tobacco as regular cigarettes. The mislabeling could have led smokers to compensate for the lower advertised nicotine level by inhaling more deeply.

Marlboro Lights are the best-selling cigarettes in Missouri, and about 700 million packs were sold between 1995 and 2002, the period of time the lawsuit covers.

Philip Morris attorney Beth Wilkinson argued that Marlboro Lights include 11 percent less tobacco, more ventilation and a longer filter than regular Marlboro Red cigarettes. She also said it was no secret among public health professionals that consumers may inhale more deeply with light cigarettes.

Plaintiffs estimate damages at around $1 billion. The trial is expected to continue through Thanksgiving.